1. Field of the Disclosure
The disclosure relates to a liquid crystal display device, and more particularly, to a backlight unit for a liquid crystal display device having a light-emitting diode (LED) light source.
2. Discussion of the Related Art
With the progress of information technology and mobile communication technology, display devices for visually showing the information have been developed. The display devices are classified into an emissive type and a non-emissive type depending on their light emission capability. Liquid crystal display (LCD) devices are non-emissive type display devices.
LCD devices require an additional light source because the LCD devices are not self-luminescent. Therefore, a backlight unit is disposed at a rear side of a liquid crystal (LC) panel and emits light into the LC panel, whereby discernible images can be displayed.
Backlight units include cold cathode fluorescent lamps (CCFLs), external electrode fluorescent lamps (EEFLs), and light emitting diodes (LEDs) as a light source. Among these, LED lamps have been widely used due to their small sizes, low power consumption, and high reliability.
Backlight units are classified into an edge type and a direct type according to the position of a light source with respect to a display panel. In edge-type backlit units, one or a pair of lamps are disposed at one side or each of two sides of a light guide plate of a backlight unit. In direct-type backlight units, a plurality of lamps are disposed directly under a display panel.
Recently, to satisfy needs of consumers, large-sized LCD device have been actively researched and developed. The direct-type backlight units are appropriate to the large-sized LCD device for the edge-type backlight units.
FIG. 1 is a cross-sectional view illustrating a liquid crystal display (LCD) module including a direct-type backlight unit and having LEDs as a light source according to the related art.
In FIG. 1, the related art LCD module includes a liquid crystal panel 10 and a backlight unit 20. The liquid crystal panel 10 includes first and second substrates 12 and 14.
The backlight unit 20 includes a reflection plate 22, LEDs 30 arranged over the reflection plate 22, and a plurality of optical sheets 26 over the LEDs 30. The plurality of optical sheets 26 includes a diffusion sheet and a light-concentrating sheet.
Here, lights emanated from adjacent two or three LEDs 30 are overlapped and mixed with each other and then are provided to the liquid crystal panel 10 as a plane light source.
The liquid crystal panel 10 and the backlight unit 20 are modularized by the top cover 60, the support main 50 and the cover bottom 70. That is, edges of the liquid crystal panel 10 and the backlight unit 20 are surrounded by the support main 50 having a rectangular frame shape. The top cover 60 covers edges of the front surface of the liquid crystal panel 10, and the cover bottom 70 covers a rear surface of the backlight unit 20. The top cover 60 and the cover bottom 70 are combined to with the support main 50 to thereby constitute one-united body.
LCD devices have been widely used as monitors for desktop computers and wall-mount televisions as well as monitors for laptop computers. LCD devices having a large display area and thin thickness have been researched and developed. Accordingly, trials of reducing a distance A between the LEDs 30 and the optical sheets 26 of the backlight unit 20 have been suggested and developed to provide large and thin LCD devices.
However, to provide the liquid crystal panel with a high quality plane light source from the backlight unit 20, various optical designs should be considered. Among the designs, it is important to appropriately maintain the distance A between the LEDs 30 and the optical sheets 26.
Specifically, in case of LEDs 30 emitting lights within a range of predetermined angles, lights emanated from adjacent two or three LEDs 30 are overlapped and mixed with each other and then are provided to the liquid crystal panel 10 as a plane light source. As shown in FIG. 2, when the distance A between the LEDs 30 and the optical sheets 26 is considerably short, there are hot spots corresponding to the LEDs 30, and there exist darkness areas between the LEDs 30 where the lights from the LEDs 30 are not overlapped and mixed with each other. This causes lamp mura phenomenon, and display qualities of the LCD device are lowered due to non-uniform brightness.
To solve the problem, if a distance between adjacent LEDs 30 is decreased, costs are increased due to an increase in the number of LEDs, and the power consumption is also raised.